DESCRIPTION: Aerosol samplers remain important through their role in the assessment (and hence control) of workers' exposures to airborne particles. Respiratory ill-health, including asthma and chronic obstructive pulmonary disease, remain major NORA priority areas. The proposed research is a continuation of a body of work carried out under RO1-OH 02984-02 (1994-1998), and then 5 RO1-OH 03687-03 (1998-2002) and 5 RO1 OH 02984-06 (1999-2003), complementing field studies supported from other resources. This new project will contain further laboratory research to develop meaningful aerosol sampling methodology under realistically low windspeed conditions not covered by previous research (0.05 to 0.5 m/s). The specific aims are to: a) develop a novel laboratory-based experimental system by which to evaluate aerosol samplers at the low windspeeds found in most workplaces; (b) use it to evaluate cascade impactor- based aerosol sampling systems that will provide information about the particle size distributions in workers' aerosol exposures; (c) define the efficiency of human inhalation (using a mannequin) at very low windspeed, allowing for the effects of the breathing patterns of the subject and body heat; (d) characterize the performances of a range of candidate personal inhalable aerosol samplers when used under such conditions; and (e) use such performance information to explain the mass biases between different samplers when they are used in realistic laboratory environments (and to relate the conclusions to what is observed in field studies). Earlier work has been influential in the setting of occupational exposure standards and in establishing relevant exposure assessment methods. Yet there remain considerable knowledge gaps. We are still unable to explain the extent to which specific personal samplers reflect actual worker exposure, or to explain differences between workplace exposure assessments using various recommended samplers. The new research will fill these gaps and place occupational aerosol exposure assessment on a still firmer footing.